Fix missing "Poor" label on the average response-time gauge

`RadialAvgResponse` maps the response-time palette to a qualitative word:

    const palette = getResponseTimeColor(avg);
    const msg: Record<string, string> = {
        success: "Excellent",
        warning: "Average",
        danger: "Poor",
    };
    ...
    {msg[palette]}

But `getResponseTimeColor` only ever returns `"success" | "warning" | "error"`
(MonitorUtils.ts) — never `"danger"`. So for the slow case `palette` is
`"error"`, `msg["error"]` is `undefined`, and no label renders. The same
component uses `theme.palette[palette].main`, which works precisely because
`palette` is the real MUI key `"error"`; every other palette helper in
MonitorUtils.ts also uses `"error"`, and `"danger"` appears nowhere else in
the client. Any monitor whose average response time is >= 300 ms shows an
empty label exactly where the "Poor" signal matters most. Use the `error`
key.

client/src/Components/monitors/charts/RadialAvgResponse.tsx

@@ -20,7 +20,7 @@ export const RadialAvgResponse = ({ avg, max }: { avg: number; max: number }) =>
 	const msg: Record<string, string> = {
 		success: "Excellent",
 		warning: "Average",
-		danger: "Poor",
+		error: "Poor",
 	};
 
 	return (